In flat panel display technologies, organic light-emitting diode (OLED) displays have many advantages, such as being light in weight, being thin, active emitting, fast responding rates, wide viewing angles, wide color gamut, high brightness, low power consumption, and so on, and have gradually become a third generation display technology after liquid crystal displays (LCDs). Compared to LCDs, OLED displays have advantages of higher power-saving, being thinner, and wider viewing angles, and therefore the OLED displays are unparalleled. At present, people have increasing demands on the degree of details of displaying, i.e., resolution. However, production of OLED display screens with high quality and high resolution still faces many challenges.
Currently, more commonly used touch technologies include an external touch technology and an in-cell touch technology. The in-cell touch technology integrates a touch sensor into a display panel. Since the in-cell touch technology can make a display device lighter and thinner than the external touch technology, the in-cell touch technology draws more attention in applying in OLED display devices. Taking a liquid crystal panel as an example. The external touch technology is a method of embedding a touch screen between a color filter substrate and a polarizer of a display screen, that is, a touch sensor is mounted in the liquid crystal panel. Compared with the in-cell touch technology, the external touch technology has much less difficulty.
With rapid development of a flexible display OLED technology, the touch screen required to be matched also needs to be flexible and foldable. A traditional touch screen needs to be separately fabricated, and then adhered to an upper surface of an OLED through an optical transparent adhesive to form a complete touch display module. An adhering process is increased, and an overall thickness is also increased simultaneously, which is unfavorable to an overall thinness and lightness of a flexible touch display screen.
In the development of an existing external OLED touch display technology, the touch sensor is generally fabricated on an OLED layer. A specific process is as follows: firstly, a thin film transistor (TFT) layer including the substrate is fabricated, and a source/drain (SD) electrode layer in the TFT layer includes a touch line and a bonding pad for a touch portion in a bonding region. Then, the OLED layer is fabricated on the TFT layer, and finally a touch layer is fabricated on the OLED layer, wherein the touch layer includes a first insulating layer, a bridging point layer, a second insulating layer, an electrode circuit layer, and a protective layer disposed from bottom to top in sequence, wherein the bridging point layer includes a plurality of metal bridges in a pixel region, and the electrode circuit layer includes a touch driving electrode, a touch sensing electrode, and a touch connecting wire. The touch driving electrode or the touch sensing electrode is connected to the metal bridges through a first contact hole penetrating the second insulating layer, and the touch connecting wire passes through a second contact holes penetrating the first insulating layer and the second insulating layer to connect with the touch lines in the bonding region. Then, in an etching process, since the pixel region and a metal bonding region need different etching depths, the prior art generally uses two photomasks to respectively etch the first insulating layer and the second insulating layer in the touch layer, so as to form vias with different depths in two ends of each of the metal bridges and in the metal bonding region. Therefore, an existing touch layer fabricating process requires at least five mask processes, but after each of the mask processes is completed, a portion of the SD layer for the touch lines and the bonding pad are etched and then exposed, so as to cause a surface of the SD layer damaged or oxidized, and electrical properties being reduced or even failed.
In addition, due to the hydrophobic nature of the OLED, when the touch layer is fabricated on the OLED layer, the OLED layer should be prevented from being excessively exposed to a wet etching process. However, a conventional etching process in the touch technology mainly adopts a wet process. Although a dry process can avoid a wet exposing, it also brings other technical problems, especially when fabricating the touch layer on a flexible OLED, in order to protect the structure, it is also necessary to consider the effect of a pre-protection process.